Coaxial thermocouple wire

ABSTRACT

A flexible coaxial thermocouple wire comprising an insulated inner thermoelement and a braided outer thermoelement surrounding the insulation covering the inner thermoelement. The braided outer thermoelement, in addition to forming one conductor of a thermocouple pair, also serves to protect and contain the insulation. Also encompassed is the formation of a thermojunction at one end of the coaxial thermocouple wire and connection of a termination to the other end.

This invention relates generally to a coaxial thermocouple wire andassociated thermojunction and termination.

As utilized herein, a "thermoelement" is one conductor of a pair ofdissimilar conductors which may be joined to form a thermocouple.Accordingly, a "thermocouple pair" comprises two "thermoelements" madeof different thermoelectric materials.

BACKGROUND

Thermocouple wire traditionally is composed of two separate wireconductors, each wire conductor being one thermoelement of athermocouple pair. Each wire conductor generally is insulated by someform of insulating material to separate it from the other wire conductorand to provide some protection from the surrounding environment. Theinsulated wire conductors may be twisted together to form thethermocouple pair, but more typically both wire conductors are containedby an overall covering or jacket of some additional insulating and/orprotective material. The outer layer or jacket not only combines the twoinsulated wire conductors into the thermocouple pair, but also serves toprotect the underlying insulations. As will be appreciated, each layerof insulation and/or protective covering applied to the thermocouplepair adds significantly to the size and cost of the completed wire.

It is also known to provide a thermocouple wire having an outer metalsheath containing densely compacted ceramic insulation and a wireconductor embedded within the ceramic insulation, with the wireconductor and outer metal sheath being used as respective thermoelementsof a thermocouple pair. One such type of thermocouple wire or cable issold under the trademark XACTPAK by the Claud S. Gordon Company,Richmond, Ill. Typically, such cable, although bendable, is relativelystiff and cannot be sharply bent without significantly disrupting theceramic insulation.

SUMMARY OF THE INVENTION

The present invention provides a flexible coaxial thermocouple wirewhich is relatively small in size, inexpensive and easy to fabricate dueto fewer operations and less material consumption. Briefly, thethermocouple wire comprises an insulated inner thermoelement and abraided outer thermoelement surrounding the insulation covering theinner thermoelement. The braided outer thermoelement, in addition toforming one conductor of a thermocouple pair, also protects and containsthe insulation which may for example be easily disturbed, loose fiberinsulation. The wire also may have an outer insulating and/or protectivejacket covering the braided outer thermoelement.

The present invention also encompasses the formation of a thermojunctionat one end of the coaxial thermocouple wire and connection of atermination to the other or cold junction end of the wire. The innerthermoelement and braided outer thermoelement may be joined togetherupon removal of a portion of the inner insulation therebetween bytwisting the braided outer thermoelement tightly around the innerthermoelement to form the thermojunction. For a thermojunction ofgreater integrity, the twisted wire braid of the outer thermoelement canbe either welded or brazed to the inner thermoelement. At the wire endopposite the thermojunction, the insulated inner thermoelement may bepulled through the wire braid of the outer thermoelement and stripped ofinsulation for connection to one terminal of the termination with thethen empty braided wire strands of the outer thermoelement being twistedand secured to the other terminal.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawing setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the invention may beemployed.

BRIEF DESCRIPTION OF THE DRAWING

In the annexed drawing:

FIG. 1 is a fragmented plan view, partially broken away and in section,of a coaxial thermocouple wire according to the invention;

FIG. 2 is a fragmented plan view, partly broken away, of the coaxialthermocouple wire with an outer jacket;

FIG. 3 is a fragmented plan view showing a thermojunction formed at oneend of the coaxial thermocouple wire; and

FIG. 4 is a fragmented plan view, partly broken away, showing atermination connected to the wire end opposite the thermojunction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in detail to the drawing and initially to FIG. 1, acoaxial thermocouple wire according to the invention is designatedgenerally by reference numeral 10. As shown, the wire 10 comprises aninner wire conductor 11 covered by a layer of insulation 12 which is inturn surrounded by an outer braid of conductive wire strands 13. Theinner wire conductor 11 and outer braid 13 respectively form the twothermoelements of a thermocouple pair and, accordingly, are made ofdissimilar but compatible thermoelectric materials. The size of eachindividual strand of the outer braided thermoelement 13 need only becompatible with the braiding operation and the overall size of the braidcompatible with the size of the inner wire conductor 11 which may be ofconventional size and type.

In addition to forming one of the two thermoelements of a thermocouplepair, the outer braid 13 assists in protecting and containing theinsulation 12 which for example may consist of easily disturbed, looseglass fiber insulation which is particularly suitable for hightemperature use applications. The braid in effect acts as a binder forholding the loose glass fiber in place. However, it should be noted thatany suitable electrically insulating material may be used as theinsulation and applied in any wall thickness compatible with thethermoelements being separated thereby.

Depending on use requirements, an outer jacket or covering 14 may alsobe provided over the braided thermoelement 13 as seen in FIG. 2. Suchjacket may be a layer of insulating material and serves to electricallyinsulate and/or protect the braided thermoelement from the exteriorenvironment. Also, the jacket may be used to provide thermocouple wirecoding information for identification purposes.

Referring now to FIG.3, a hot or measuring junction formed at one end ofthe thermocouple wire 10 is indicated at 15. The measuring junction 15can be easily formed by flaring back the braided thermoelement 13 at oneend of the wire to permit removal of an end portion of the insulation12. Then the end of the braided thermoelement free of insulation can betwisted tightly around the bare end of the inner thermoelement or wireconductor 11 as shown. For a thermojunction of greater integrity, thetwisted wire braid can be either welded or brazed to the inner wireconductor.

As seen in FIG. 4, the other or cold junction end of the thermocouplewire 10 opposite the measuring junction 15 may be connected to atermination 16. Any convenient termination can be used in conjunctionwith the wire such as the illustrated plug having prongs 17 and 18 andassociated terminals 19 and 20 to which the inner and outerthermoelements 11 and 13 are connected, respectively. To effect suchconnection, the insulated inner thermoelement 11 and inner insulation 12can be passed through the braided thermoelement 13 at some distance fromthe end of the braided thermoelement to provide a free end portionthereof and an empty end portion of the braided thermoelement 13. Afterwithdrawal from the braid 13, the emergent end of the innerthermoelement 11 then can be stripped of its insulation for connectionto the terminal 20 by a suitable fastener 22 and the empty end of thebraided thermoelement 13 twisted and connected to the other terminal 19by a fastener 21. If desired, the separated end portions of theinsulated inner thermoelement 11 and braided outer thermoelement 13 maybe held together for a portion of their length by a short tubular sleeve23 fitted thereover to provide stress relief at the wire terminationjunction.

Although the invention has been shown and described with respect tocertain preferred embodiments, it is obvious that equivalent alterationsand modifications will occur to others skilled in the art upon thereading and understanding of this specification. The present inventionincludes all such equivalent alterations and modifications, and islimited only by the scope of the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A coaxial thermocouplewire comprising an inner thermoelement, a layer of insulation coveringsaid inner thermoelement, and a braided outer thermoelement surroundingsaid insulation covering said inner thermoelement, said innerthermoelement and braided outer thermoelement being joined at one end ofsaid wire to form a measuring junction.
 2. A thermocouple wire as setforth in claim 1, further comprising an outer insulating jacket coveringsaid braided outer thermoelement.
 3. A thermocouple wire as set forth inclaim 1, wherein said insulation consists of a layer of loose fiberinsulating material contained and protected by said braided outerthermoelement.
 4. A thermocouple wire as set forth in claim 1, whereinsaid braided outer thermoelement is twisted tightly around said innerthermoelement at said measuring junction.
 5. A thermocouple wire as setforth in claim 1, wherein said insulated inner thermoelement, at the endof said wire opposite said measuring junction, extends through andemerges from said braided outer thermoelement for connection to atermination.
 6. A thermocouple wire as set forth in claim 5, wherein theemergent end of said insulated inner thermoelement is stripped ofinsulation and connected to one terminal of said termination, and theend of said braided outer thermoelement extending beyond such emergentend is connected to another terminal of said termination.
 7. A coaxialthermocouple wire comprising an inner wire conductor, a layer ofinsulation covering said inner wire conductor, and a braid of conductivewire strands closely surrounding and containing said insulation, saidinner conductor and wire strands being made of dissimilar thermoelectricmaterials suited for joinder to form a thermojunction, said innerconductor and wire strands being joined at one end of said innerconductor to form said thermojunction.
 8. A thermocouple wire as setforth in claim 7, further comprising an outer insulating jacket coveringsaid braid of conductive wire strands.
 9. A thermocouple wire as setforth in claim 4, wherein said braided outer thermoelement is welded orbrazed to said inner thermoelement at said measuring junction.
 10. Athermocouple wire as set forth in claim 7, wherein said insulated innerwire conductor, at the end opposite said thermojunction, extends throughand emerges from said braid of conductive wire strands for connection toa termination.
 11. A thermocouple wire as set forth in claim 10, whereinthe emergent end of said insulated inner wire conductor is stripped ofinsulation and connected to one terminal of said termination, and theend of said braid of conductive wire strands extending beyond suchemergent end is connected to another terminal of said termination.